Moisture-resistant electronic device package and methods of assembly

ABSTRACT

Various embodiments for moisture-resistant image sensor packaging structures and methods of assembly are disclosed. Image sensor packages of the present invention include an interposer, a housing structure formed on the interposer for surrounding an image sensor chip, and a transparent cover. The housing structure may cover substantially all of the interposer chip surface. In another embodiment, the housing structure also covers substantially all of the interposer edge surfaces. The housing structure may also cover substantially all of the interposer attachment surface. An image sensor chip is electrically connected to the interposer with sealed wire bond connections or with sealed flip-chip connections. The housing structure may include runners that enable simultaneous sealing of the interior of the image sensor package and of the transparent cover.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 10/663,959,filed Sep. 16, 2003, now U.S. Pat. No. 6,953,891, issued Oct. 11, 2005.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to packaging of electronicdevices for protection from external environmental conditions. Moreparticularly, the present invention relates to moisture-resistantpackages with transparent covers for enclosing solid-state image sensorsor similar electronic devices that are sensitive to light or other formsof radiation.

2. State of the Art

Solid-state image sensors, for example, charge coupled devices (CCDs) orcomplementary metal-oxide semiconductor (CMOS) chips, are increasinglyin demand for use with electronic products such as digital cameras.Conventionally, these sensors have been packaged for use by mountingthem to a substrate and enclosing them within a housing assembly. Thehousing assembly incorporates a transparent lid to allow light or otherforms of radiation to be received by the sensor. The lid may be a flatwindow or shaped as a lens to provide optical properties. The substrateand housing are often formed from a ceramic material, and the lid isglass or a similar transparent substance attached to the housing by anadhesive. Due to the materials and structure involved, this packagingtechnique may be expensive and difficult to manufacture.

In order to overcome these problems, various methods have been developedin attempts to simplify the construction of image sensor packages andreduce material costs. One such approach has been to fabricate packagesby using molded housing assemblies that are attached to, or formed on,substrates of low-cost materials like BT/epoxy laminates or plastic.Examples include U.S. Pat. No. 5,811,799 to Wu and U.S. Pat. No.6,266,197 to Glenn et al. U.S. Pat. No. 6,906,403, issued Jun. 14, 2005,and pending U.S. patent application Ser. No. 10/228,411, filed Aug. 26,2002, both assigned to the assignee of the present invention, alsodisclose image sensor packages of this type.

While these and other designs have been beneficial with respect toreducing the cost of manufacturing, they raise other concerns. Imagesensor packages constructed from materials such as those described abovemay not provide the same hermetic sealing capabilities as prior artceramic packaging. Glass laminate-type substrates, for instance, are notcompletely impermeable and may absorb moisture, especially at edgelocations where minute gaps between laminate layers are exposed to theoutside environment. This moisture may ultimately find its way into theinterior of the package, resulting in damage to the image sensorcircuitry. Moisture absorption may also cause deformations in thesubstrate that will negatively affect the focal properties of thepackage. Another problem arises from the use of a molded housing, whichdoes not have the high dimensional tolerances of ceramics and may causedifficulties with sealing to the substrate and transparent lid.

The increasing number of portable electronic products intended for usein extreme environments makes reliable sealing of image sensors an evenmore important aspect of any packaging structure. What is needed is animage sensor package that is simple and inexpensive to manufacture, andthat also provides reliable hermetic sealing capabilities to preventmoisture damage and other harmful environmental effects.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, improved packages forelectronic devices and methods for their assembly are disclosed.Embodiments of the present invention are directed to image sensor chips.However, packaging of any other light or radiation-sensitive electroniccomponents is also contemplated as being within the scope of the presentinvention. In a basic form, an image sensor package according to thepresent invention comprises a housing structure formed on an interposersubstrate by molding or other deposition process. The chips are mountedin a chip cavity formed by the housing structure and electricallyconnected to interposer contact pads that are exposed through thehousing structure within the chip cavity. The chip cavity is then sealedby a transparent cover which acts as a window or lens. Once assembled,the image sensor package may be incorporated into electronic devices byconnection to external attachment pads on the interposer. The packagesare inexpensive and simple to construct while exhibiting durability andimproved sealing properties.

In one embodiment according to the present invention, an image sensorpackage is assembled by forming a housing structure that coverssubstantially the entire chip surface of the interposer, leaving only asmall area of the chip surface immediately surrounding the interposercontact pads exposed through apertures within the housing structure forconnection to the image sensor chip. As used herein, the term “chipsurface” refers to the side of the interposer on which image sensorchips are mounted within the chip cavity.

In another embodiment according to the present invention, the interposermay also include peripheral structures in the form of tie bars or otherprotrusions that extend from the edge surfaces of the interposer. Thetie bars provide spacing to enable mold material to cover the edgesurfaces of the interposer when forming the housing structure. The tiebars may also be used to connect a strip or array of interposers,thereby enabling multiple housing structures to be formed simultaneouslyon a single substrate and subsequently separated into individual imagesensor packages.

In another embodiment according to the present invention, the housingstructure also covers substantially the entire attachment surface of theinterposer, leaving only the area of the attachment surface immediatelysurrounding the external attachment pads exposed. As used herein, theterm “attachment surface” refers to the side of the interposer which isopposite the chip surface of the interposer.

In another embodiment according to the present invention, bond pads ofthe image sensor chip are attached directly to the interposer contactpads exposed through the apertures in the housing structure with wirebonds. The apertures may optionally be filled with a liquid sealant tofurther seal the interposer from the chip cavity.

In another embodiment according to the present invention, the aperturesthat expose the interposer contact pads are first filled with aconductive material up to a level that is substantially even with thebottom of the chip cavity. In this manner, the contact pads are built upto further seal the interposer from the chip cavity. Bond wires may thenbe attached to the built-up pads at a level that is substantially evenwith the bottom of the chip cavity, rather than in the relatively smallspace provided by the apertures in the housing structure exposing thecontact pads. A liquid sealant may also be applied to further seal theconnection between the built-up pads and the bond wires.

In an alternative to the above embodiment, the bond pads of the imagesensor chip are attached directly to the built-up pads in a flip-chipmanner, such that bond wires are not required. A liquid sealant may beapplied under the image sensor chip in a capillary process to furtherseal the connection between the image sensor bond pads and the built-uppads.

In another embodiment according to the present invention, the housingstructure is provided with runners that enable sealing the bottom of thechip cavity simultaneously with sealing the transparent cover to thehousing structure. Under this embodiment, a ledge surrounding the chipcavity for supporting edges of the transparent cover acts as a runnerfor a sealant that fills the space between the edges of the transparentcover and the molded housing structure. At least one additional runneris formed by a channel that extends from the ledge down to the bottomsurface of the chip cavity. After the transparent cover is placed on theledge of the housing structure, a liquid sealant is injected into asealing well formed in the housing structure adjacent to the runnerareas. Capillary flow of the liquid sealant along the ledge fills thespace between the edges of the transparent cover and the housingstructure. At the same time, capillary flow of the liquid sealant alongthe additional runner or runners covers the bottom surface of the chipcavity to seal any exposed areas of the interposer.

Other and further features and advantages will be apparent from thefollowing descriptions of the various embodiments of the presentinvention when read in conjunction with the accompanying drawings. Itshould be understood that the following descriptions are provided forillustrative and exemplary purposes only, and that numerous combinationsof the elements of the various embodiments of the present invention arepossible.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be thebest mode for carrying out the invention:

FIG. 1 is a cross-sectional side view of an image sensor packageinterposer according to the present invention.

FIG. 2A is a cross-sectional side view of a first embodiment of apackage structure according to the present invention.

FIG. 2B is a bottom view of the package structure depicted in FIG. 2A.

FIG. 2C is a top view of the package structure depicted in FIG. 2A.

FIG. 3 shows a molding process for forming the package structuredepicted in FIG. 2A.

FIG. 4A is a top view of an image sensor package interposer according toa second embodiment of the present invention.

FIG. 4B is a bottom view of a package structure according to the secondembodiment of the present invention.

FIG. 4C is a bottom perspective view of the package structure depictedin FIG. 4B.

FIG. 5 is a bottom perspective view of a package structure according toa third embodiment of the present invention.

FIG. 6 shows a molding process for forming the package structuredepicted in FIG. 5.

FIG. 7A is a cross-sectional side view of a package structure accordingto a fourth embodiment of the present invention.

FIG. 7B is an enlarged sectional view of the package structure depictedin FIG. 7A.

FIG. 7C is a cross-sectional side view of an image sensor packageaccording to the fourth embodiment of the present invention.

FIG. 7D is an enlarged sectional view of the packaged structure depictedin FIG. 7A including an optional sealant.

FIG. 8A shows an enlarged sectional view of a package structureaccording to a fifth embodiment of the present invention.

FIG. 8B shows an enlarged sectional view of an alternative packagestructure according to the fifth embodiment of the present invention.

FIG. 9A is a cross-sectional side view of a flip-chip-configured imagesensor package according to the fifth embodiment of the presentinvention.

FIG. 9B is an enlarged sectional view of the image sensor packagedepicted in FIG. 9A.

FIG. 10 is a top view of a package structure according to a sixthembodiment of the present invention.

FIG. 11 is an enlarged sectional view showing a channel formed in thepackage structure depicted in FIG. 10.

FIGS. 12A–12D and 13 show a process for assembling and sealing an imagesensor package according to the sixth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

As described below, the present invention includes package structuresand methods of package assembly for image sensors such as solid stateCCD or CMOS chips for receiving an image of reflected light or otherelectromagnetic radiation from one or more objects. However, thepackages and methods of the present invention would also work well forenclosing other types of light or other radiation-sensitive electroniccomponents such as, for example, erasable programmable read-only memorychips (EPROMs).

Referring initially to the accompanying drawings, various aspects of thepresent invention are illustrated to show exemplary image sensor packagestructures and methods for their assembly. To simplify the descriptionof the present invention, common elements of the various embodimentsillustrated by the drawings are designated with like reference numerals.The figures presented by the drawings are not meant to be illustrativeof actual views of any particular portion of a particular image sensorpackage structure, but are merely idealized schematic representationswhich are employed to assist in clearly and fully describing theinvention.

FIG. 1 shows an interposer 2 that is utilized as a platform for thesubsequent formation of image sensor package embodiments of the presentinvention. Interposer 2 includes a chip surface 4, an opposingattachment surface 6, and peripheral edge surfaces 8. Contact pads 10are formed on chip surface 4 for wire bond or flip-chip connection to animage sensor chip as described in further detail below. Internalconductive elements 12 electrically connect contact pads 10 toattachment pads 14 on attachment surface 6 for connecting a completedimage sensor package to a larger assembly such as a printed circuitboard. Interposer 2 may be formed of materials such as FR-4 and BTlaminates or even plastic, which are less expensive and easier tomanufacture than the ceramic substrates typically used for image sensorpackages. Of course, any conventional substrate materials, includingceramic, may be used to form interposer 2 if necessary or desirablebased on other considerations besides cost. While interposer 2 isillustrated as being configured for assembly of a single image sensorpackage, it may also be formed as part of a larger substrate comprisingmultiple interposers. In this manner, several image sensor packages canbe formed simultaneously on a single substrate, which is then singulatedto provide individual image sensor packages.

Turning to FIGS. 2A–2C, a first embodiment of an image sensor packageaccording to the present invention is illustrated. As seen in FIG. 2A, ahousing structure 16 is formed on interposer 2 that covers substantiallyall of chip surface 4. Housing structure 16 has raised sidewalls 18around the perimeter of interposer 2, thereby forming a chip cavity 20for receiving an image sensor chip. Sidewalls 18 include a ledge 22 thatsurrounds chip cavity 20 for receiving and supporting a transparentcover 46 (FIG. 7C). Housing structure 16 also extends across the bottomsurface 24 of chip cavity 20 and includes apertures 26 for exposingcontact pads 10 of interposer 2.

FIG. 2B shows a bottom view of interposer 2 with attachment pads 14positioned around the perimeter of attachment surface 6. It should beunderstood that the location and shape of attachment pads 14 illustratedin FIG. 2B are only exemplary, and that any other known pad layout ispossible. Image sensor packages requiring a high number of I/Oconnections, for instance, may have a matrix of attachment pads formedin an array pattern on attachment surface 6. Rather than beingrectangular, attachment pads 14 might also have a circular shape toreceive ball or spherically shaped external conductive elements.

FIGS. 2A and 2B show that in the current embodiment, housing structure16 does not cover attachment surface 6 or edge surfaces 8 of interposer2, but is instead limited to covering chip surface 4 in the manner shownby FIG. 2C. As seen in FIG. 2C, the area of interposer 2 at the bottomof chip cavity 20 is entirely covered by housing structure 16 except forlocations where apertures 26 are formed to expose contact pads 10. FIG.2C illustrates that contact pads 10 are positioned in rows with a singleaperture 26 exposing an entire row of contact pads. It is also possiblethat an aperture 26 may be provided for each contact pad, with materialfrom housing structure 16 covering areas between adjacent contact pads.

Housing structure 16 may be formed on interposer 2 using conventionalmolding processes such as transfer molding, pot molding, or injectionmolding. FIG. 3 shows an example of how housing structure 16 may beformed by a molding process. A molding tool 28 is provided having alower platen 28 a and an upper platen 28 b. Lower platen 28 a includes amold cavity 30 a which holds interposer 2 in sealing relationshipagainst attachment surface 6 and edge surfaces 8. Upper platen 28 bincludes a mold cavity 30 b that is positioned over chip surface 4. Asseen in FIG. 3, mold cavity 30 b includes protrusions 32 that sealagainst contact pads 10 to form apertures 26 in housing structure 16.Mold cavity 30 b is then filled with a mold compound 34 in a liquid orotherwise molten state. Mold compound 34 is cured to an at leastsemisolid state, and interposer 2 is removed from molding tool 28,leaving the housing structure 16 illustrated in FIGS. 2A–2C.

In the situation where interposer 2 is formed as part of a largersubstrate containing multiple interposers, mold cavities 30 a and 30 bmay be configured with a size and shape to form a housing structure ontothe chip surface of each interposer, with subsequent singulation of thelarger substrate providing individual image sensor packages. It is alsopossible that housing structure 16 could be premolded and then attachedto interposer 2 with a layer of suitable adhesive material applied toone or both of chip surface 4 and housing structure 16.

Mold compound 34 may be a thermoplastic polymer or other suitableencapsulant material as known in the art. Further, a filler materialsuch as fine silicon particles may be incorporated within the moldcompound 34 to reduce cost, also as known in the art. Other suitableknown materials for mold compounds include, without limitation,thermoset polymers and epoxy compounds. Any other molding compounds maybe employed to form housing structure 16, however, it is desirable touse a material that exhibits low moisture absorption and a CTE(coefficient of thermal expansion) having a minimal difference from thatof interposer 2 and transparent cover 46 (FIG. 7C).

FIGS. 4A–4C show a second embodiment of an image sensor packageaccording to the present invention. As seen in FIG. 4A, with the secondembodiment, interposer 2 includes tie bars 36 that protrude from edgesurfaces 8. Tie bars 36 provide spacing to enable mold compound 34 tocover edge surfaces 8 of interposer 2 during package formation. With themolding process illustrated in FIG. 3, for instance, tie bars 36 wouldabut against the sides of mold cavity 30 a in lower platen 28 a tocenter interposer 2 within mold cavity 30 a. When mold cavity 30 b isfilled, mold compound 34 enters the areas between the sides of moldcavity 30 a and edge surfaces 8 of interposer 2. After curing moldcompound 34, interposer 2 is removed from molding tool 28, leaving ahousing structure 16′ that covers and seals chip surface 4 and all ofedge surfaces 8 except for the outer ends of tie bars 36, as illustratedby FIGS. 4B and 4C.

The second image sensor package embodiment is well suited for situationswhere interposer 2 comprises a laminate-type substrate with minute gapsbetween laminate layers that are exposed to the outside environment andmay absorb moisture. The second embodiment is also applicable whereinterposer 2 is formed as part of a larger substrate containing multipleinterposers. For example, slots or openings may be formed in the largersubstrate at locations between interposer 2, leaving portions ofsubstrate material between the interposers to act as tie bars 36. Inthis manner, tie bars 36 hold the interposers together while enablingmold compound 34 to cover edge surfaces 8 of all the interposers. Oncepackage formation is complete, the cured molding compound 34 and tiebars 36 between adjacent interposers 2 are cut or otherwise separated toprovide individual image sensor packages.

In some instances, it may be desirable to seal all of the surfaces ofinterposer 2 from the outside environment. Such sealing not only helpsprevent moisture from entering chip cavity 20, but also further limitsany moisture that may be absorbed by interposer 2. Moisture absorptionby interposer 2 is a concern as it may cause warping or otherdeformations in shape that will negatively affect the focal propertiesof a completed image sensor package. FIG. 5 shows a third embodiment ofan image sensor package according to the present invention thataddresses this problem. As seen in FIG. 5, with the third embodiment, ahousing structure 16″ is formed on interposer 2 that coverssubstantially all of chip surface 4 and edge surfaces 8, and also coverssubstantially the entire attachment surface 6 of the interposer 2,leaving only the external attachment pads 14 exposed.

FIG. 6 shows an exemplary molding process for forming housing structure16″. According to the third embodiment, molding tool 28 is modified suchthat lower platen 28 a has a mold cavity 30 a′ that does not sealagainst attachment surface 6 of interposer 2. Instead, mold cavity 30 a′includes protrusions 38 that raise interposer 2 up from the bottom ofmold cavity 30 a′ and seal against attachment pads 14. As in the secondembodiment, interposer 2 has tie bars 36 that abut against the sides ofmold cavity 30 a′ in lower platen 28 a to center interposer 2 withinmold cavity 30 a′. When mold cavity 30 b is filled, mold compound 34passes through the areas between the sides of mold cavity 30 a′ and edgesurfaces 8 of interposer 2, thereby filling the bottom of mold cavity 30a′ and covering attachment surface 6. After curing mold compound 34,interposer 2 is removed from molding tool 28, leaving housing structure16″ that covers and seals substantially all of chip surface 4, edgesurfaces 8, and attachment surface 6 as illustrated by FIG. 5.

Where interposer 2 is formed as part of a larger substrate containingmultiple interposers, tie bars 36 may be formed in the same manner asdescribed in the second embodiment and used to hold the interposerstogether during the molding process. The spaces between each interposerprovide additional areas for mold compound 34 to pass into mold cavity30 a′ in order to cover attachment surface 6. When mold cavities 30 a′and 30 b are configured with a size and shape for molding largesubstrates containing multiple interposers, it may also be desirable tosupply mold compound 34 directly to mold cavity 30 a′ while filling moldcavity 30 b to ensure uniform coverage.

It will be understood by one of ordinary skill in the art that themolding processes described with respect to the above embodiments areonly exemplary, and that other methods may be used to apply moldmaterial to the various surfaces of interposer 2.

Other alternatives to forming housing structures 16–16″ are alsocontemplated by the present invention. One such alternative includesdisposing a flowable material over the surfaces of interposer 2 in oneor more sequentially cured layers to build housing structures 16–16″. Toform housing structure 16, for example, a high-viscosity liquid or gelsuch as an epoxy may be dispensed from a nozzle onto chip surface 4. Thehigh-viscosity liquid or gel is then cured to form a first hardenedlayer. An additional layer of high-viscosity liquid or gel is dispensedover the first hardened layer and cured to form second hardened layer.Subsequent layers of liquid or gel may be added, as necessary, until thedesired shape for housing structure 16 is formed. To form housingstructure 16′, the liquid or gel may simply be deposited in layers alongedge surfaces 8 while covering chip surface 4. With this method, tiebars 36 are not be required to provide mold spacing, and edge surfaces 8may be completely sealed from the outside environment. Once chip surface4 and edge surfaces 8 are covered, the same process may be used to coverattachment surface 6, thereby forming housing structure 16″.

Another example of this layering approach exists in using astereolithographic (STL) deposition process to form housing structures16–16″. As defined in the art, STL involves the formation of solidstructures by selectively curing portions of volumes of a photocurableliquid polymer or resin material contained within a tank or reservoir.Depending on the liquid material composition, curing may be accomplishedby exposure to irradiation with selected wavelengths of light or otherelectromagnetic radiation, for instance, when curing a materialsusceptible to initiation of cross-linking by exposure to ultraviolet(UV) radiation, such as through use of a UV laser beam. By curing one ormore successive layers of the liquid material, intricate solidstructures of almost any shape may be formed.

After a housing structure 16–16″ has been formed on interposer 2, animage sensor chip may be mounted within chip cavity 20. FIGS. 7A–9B showalternative embodiments of how an image sensor chip may be mountedwithin chip cavity 20 and electrically connected to contact pads 10 ofinterposer 2. While the following embodiments are described in terms ofhousing structure 16, it should be understood that they also apply tomounting of image sensor chips within housing structures 16′ and 16″.

FIGS. 7A–7D show a fourth embodiment of an image sensor packageaccording to the present invention wherein an image sensor chip 40 iswire bonded directly to contact pads 10 exposed through apertures 26 ofhousing structure 16. As seen in FIG. 7A, image sensor chip 40 isattached to the bottom surface 24 of chip cavity 20 between opposingrows of contact pads 10. Attachment of image sensor chip 40 may beaccomplished with an adhesive material (not shown) applied to one orboth of bottom surface 24 and image sensor chip 40. FIG. 7B shows thatonce image sensor chip 40 is in place, bond wires 42 are attachedbetween contact pads 10 of interposer 2 and bond pads 44 of image sensorchip 40 to provide electrical connection.

At this point, a transparent cover 46 may be set onto ledge 22 ofhousing structure 16 and sealed in place to provide a completed imagesensor package 48, as illustrated by FIG. 7C. Transparent cover 46 maybe formed of an at least partially optically transparent material suchas borosilicate glass (BSG). Of course, other types of glass, quartz oreven plastic which enable the passage of a desired range of wavelengthsof light or other forms of electromagnetic radiation may also be used.Furthermore, transparent cover 46 may be formed to provide an opticalfunction, for example, shaping its surface at locations above chipcavity 20 to provide focusing capabilities.

To secure transparent cover 46 in place and hermetically seal imagesensor chip 40 within chip cavity 20, a bead of epoxy, silicone gel orother liquid or gel adhesive sealant 50 may be applied along the edge oftransparent cover 46 as shown in FIG. 7C. If desired, a two-componentadhesive resin may be employed, with one component applied to ledge 22and the other to transparent cover 46 so that a cure will not commenceuntil the two components are in contact. Other known sealing mechanismsmay be used as well, as long as they provide a suitable hermetic bond.It is desirable, so that the optical capabilities of image sensor chip40 are not compromised, that any adhesive used be of a type which doesnot outgas volatiles or other compounds when curing. A snap-cure epoxy,as known in the art, may be suitable, as may an epoxy cured to aB-stage, or tacky state, prior to application of transparent cover 46.Another possibility is to form housing structure 16 with a runner thatprovides a space for venting gases from chip cavity 20 while adhesivesealant 50 cures, as described in further detail below.

With the fourth embodiment of the present invention, it may sometimes bedesirable to completely seal the bottom surface 24 of chip cavity 20 byfilling in apertures 26 prior to attaching transparent cover 46. FIG. 7Dshows that liquid sealant 52 is deposited within apertures 26 toaccomplish this complete sealing. Liquid sealant 52 may be any materialthat exhibits low moisture permeability and bonds well to thesurrounding housing structure 16. Conventional UV or thermally curedepoxy adhesives, for example, may be suitable for this application.

FIG. 8A shows a fifth embodiment of an image sensor package according tothe present invention where apertures 26 are first filled with aconductive material 54 up to a level that is substantially even with thebottom surface 24 of the chip cavity 20. In this manner, contact pads 10are built up to further seal interposer 2 from chip cavity 20.Furthermore, bond wires 42 may then be attached to conductive material54 at a level that is substantially even with bottom surface 24,eliminating the difficulties with having to attach a bond wire 42 withinthe relatively small space provided by apertures 26. Filling ofapertures 26 may be carried out with conventional metal depositionprocesses such as chemical-vapor deposition (CVD), depositing aconductive or conductor-filled epoxy, or simply by depositing andreflowing solder paste within apertures 26. FIG. 8B shows that in thecase where conductive material 54 is a solder paste, it may notcompletely fill apertures 26 because flux material is driven off duringreflow. In this situation, liquid sealant 52 may be deposited overconductive material 54 to completely fill apertures 26.

FIGS. 9A and 9B show an alternative to the fifth embodiment of thepresent invention wherein image sensor chip 40 is attached directly tothe built-up conductive material 54 over contact pads 10 in a flip-chipmanner, such that bond wires 42 are not required. As seen in FIG. 9A,image sensor chip 40 includes through-hole vias 56 connected tobottom-side bond pads 58 on image sensor chip 40. The formation ofthrough-hole vias 56 may be accomplished by laser cutting or etchingholes in image sensor chip 40 and filling the holes with conductivematerial. Such via formation processes are known in the art and need notbe described further with respect to carrying out the present invention.By using a flip-chip configuration, it is possible to mount a largerimage sensor chip 40 within chip cavity 20 because contact pads 10 ofinterposer 2 may be located underneath, rather than peripheral to, imagesensor chip 40. Furthermore, contact pads 10 may be positioned in anarray-type pad layout across the entire bottom surface 24 of chip cavity20, enabling image sensor chips having higher I/O requirements to bemounted within the same area.

Image sensor chip 40 is secured within chip cavity 20 by attachingbottom-side bond pads 58 to conductive material 54 with a conductivebond. A conductive adhesive material may be used for this purpose, suchas conductive or conductor-filled epoxies, or with a film ofanisotropically conductive adhesive material that is applied to coverall of the bonding areas. Alternatively, if epoxy or solder paste isused for conductive material 54, bottom-side bond pads 58 may simply beset in place and bonded to by curing the epoxy or reflowing the solderpaste. FIG. 9B shows that the flip-chip mounting embodiment mayoptionally include deposition of an underfill 60 by capillary flow of aliquid sealing material to fill gaps between bottom surface 24 of chipcavity 20 and image sensor chip 40. As known in the art, underfill 60reinforces the conductive bonds to image sensor chip 40 and seals outcontamination that may cause shorting between bond locations.

In a sixth embodiment according to the present invention, any of housingstructures 16–16″ may be provided with one or more runners that enablesealing the bottom surface 24 of chip cavity 20 simultaneously with thesealing of transparent cover 46. FIGS. 10–13 show an example of thisembodiment of the invention. While FIGS. 10–13 are described in terms ofhousing structure 16, it should be understood that the presentembodiment is also applicable to housing structures 16′ and 16″.

In the same manner as previously discussed, FIG. 10 shows that housingstructure 16 is formed with a ledge 22 surrounding chip cavity 20 forsupporting the edges of transparent cover 46 (not shown). Ledge 22 actsas a runner for adhesive sealant 50 to fill the space between the edgesof transparent cover 46 and housing structure 16. In the presentembodiment, adhesive sealant 50 comprises a liquid epoxy. However, othercurable liquid sealants suitable for deposition by capillary flow mayalso be used, as long as they are capable of forming a hermetic seal. Atleast one additional runner is formed by a channel 62 that extends fromledge 22 down to bottom surface 24 of chip cavity 20. FIG. 11 is anenlarged view of area A in FIG. 10 that more clearly shows channel 62formed to extend down a corner of chip cavity 20. FIG. 11 also showsthat a sealing well 64 is formed in housing structure 16 to provide anexpanded opening adjacent to the junction of channel 62 and ledge 22.

Turning to FIGS. 12A-13, an exemplary assembly process is illustrated toshow how the present embodiment enables simultaneous sealing of bottomsurface 24 and transparent cover 46. In FIG. 12A, an epoxy 66 or othersuitable adhesive material is deposited on bottom surface 24. In FIG.12B, image sensor chip 40 is mounted within chip cavity 20 by attachmentto epoxy 66. Once epoxy 66 has sufficiently cured, bond pads 44 on thetop of image sensor chip 40 are electrically connected to contact pads10 with bond wires 42, as shown in FIG. 12C. In FIG. 12D transparentcover 46 is placed on ledge 22 of housing structure 16. As shown by FIG.12D, sealing well 64 provides an opening at the corner of transparentcover 46 through which adhesive sealant 50 may be injected into therunner areas formed by ledge 22 and channel 62.

FIG. 13 is a sectional view of image sensor package 48 taken along line13—13 in FIG. 12D. FIG. 13 shows that after transparent cover 46 isplaced on ledge 22, adhesive sealant 50 is dispensed from a nozzle 68into sealing well 64, and by capillary action flows around the runnerarea of ledge 22 to fill the space between housing structure 16 andtransparent cover 46. At the same time, capillary flow of adhesivesealant 50 down channel 62 covers and further seals bottom surface 24 ofchip cavity 20. In this manner, adhesive sealant 50 may be used to fillapertures 26, eliminating the need to perform a separate fillingoperation with liquid sealant 52 as described above with respect to thefourth and fifth embodiments of the present invention.

In order to encourage the capillary flow of adhesive sealant 50, it maybe necessary in some situations to carry out the dispensing operationunder a vacuum applied to chip cavity 20. Once adhesive sealant 50 hasbeen dispensed to a desired level, the opening provided by sealing well64 may be filled to completely seal chip cavity 20 from the outsideenvironment. An additional benefit of this process is that while sealingwell 64 remains unfilled, volatiles or other compounds produced by thecuring of adhesive sealant 50 within chip cavity 20 may be outgassedthrough the remaining opening.

Although FIGS. 12A–13 show sealing for an image sensor package with awire-bonded configuration, this sealing structure and method may also beused for the flip-chip mounted image sensor chip 40 illustrated in FIGS.9A and 9B. In a flip-chip configuration, the capillary flow of adhesivesealant 50 fills the spaces between image sensor chip 40 and bottomsurface 24 of chip cavity 20, eliminating the need to perform a separateoperation for forming underfill 60. It should also be understood thatwhile FIGS. 12A–13 depict a single channel 62 formed along a corner ofchip cavity 20, other configurations are possible. Channel 62 andsealing well 64 may be formed at other locations along the perimeter ofledge 22, and multiple channels could be formed to allow flow ofadhesive sealant 50 down to bottom surface 24.

With the simultaneous sealing process of the present embodiment, any ofthe above-described housing structures 16–16″ may also be formed withoutcovering the area of interposer 2 underlying chip cavity 20. In thismanner, package formation is simplified because there is no requirementto wire bond within apertures 26 or to carry out additional operationsto fill them with conductive material 54. Once image sensor chip 40 ismounted and electrically connected to interposer 2, adhesive sealant 50covers any areas not sealed by the housing structures.

Although the present invention has been depicted and described withrespect to the illustrated embodiments, various additions, deletions andmodifications are contemplated within its scope. The scope of theinvention is, therefore, indicated by the appended claims rather thanthe foregoing description. Further, all changes which may fall withinthe meaning and range of equivalency of the claims and elements andfeatures thereof are to be embraced within their scope.

1. An electronic device package comprising: a substrate; a housingstructure disposed on the substrate and comprising a plurality of raisedsidewalls extending along the perimeter of the substrate defining acavity in the housing structure; a ledge on the plurality of raisedsidewalls of the housing structure and surrounding the cavity; and atleast one channel disposed within at least one sidewall of the pluralityof raised sidewalls and extending from the ledge to a bottom surface ofthe cavity.
 2. The electronic device package of claim 1, wherein thesubstrate has a first surface, an opposing second surface, and aplurality of edge surfaces extending between the first surface and thesecond surface around a perimeter of the substrate, and the housingstructure covers the plurality of edge surfaces of the substrate.
 3. Theelectronic device package of claim 2, further comprising at least oneprotrusion extending from at least one edge surface of the plurality ofedge surfaces.
 4. The electronic device package of claim 3, wherein theat least one protrusion comprises a tie bar extending perpendicularlyfrom the at least one edge surface.
 5. The electronic device package ofclaim 4, wherein the tie bar is connected to another substrate ofanother electronic device package.
 6. The electronic device package ofclaim 1, further comprising: at least one contact pad on a first surfaceof the substrate; at least one attachment pad on an opposing secondsurface of the substrate; and at least one conductive elementelectrically connecting the at least one contact pad and the at leastone attachment pad.
 7. The electronic device package of claim 6, whereinthe housing structure covers substantially all of the second surface ofthe substrate and includes at least one aperture exposing the at leastone attachment pad through the housing structure.
 8. The electronicdevice package of claim 1, wherein the housing structure comprises oneof a mold compound, an epoxy, and a photocurable polymer or resin. 9.The electronic device package of claim 6, wherein the at least onecontact pad comprises a plurality of contact pads and the at least oneaperture in the bottom surface of the cavity comprises a plurality ofapertures, each aperture of the plurality of apertures exposing a singlecontact pad of the plurality of contact pads.
 10. The electronic devicepackage of claim 1, further comprising an electronic device sensitive tolight or other radiation mounted within the cavity of the housingstructure and having at least one bond pad thereon.
 11. The electronicdevice package of claim 6, further comprising a sealing material fillinga gap between the electronic device and the bottom surface of thecavity.
 12. The electronic device package of claim 1, further comprisinga sealant material substantially filling the at least one channel. 13.The electronic device package of claim 1, further comprising a sealingwell comprising a notch in the housing structure adjacent to a junctionof the ledge and the at least one channel, the sealing well in fluidcommunication with the channel.
 14. The electronic device package ofclaim 13, further comprising a transparent cover supported by the ledgeand covering the cavity.
 15. The electronic device package of claim 14,further comprising a sealant material adhesively bonding the transparentcover to the housing structure and covering the bottom surface of thecavity.
 16. A method of forming an electronic device package comprising:providing a substrate; forming a housing structure including sidewallsdefining a cavity on the substrate; forming a ledge within thesidewalls, the ledge surrounding the cavity; forming at least onechannel extending from the ledge to a bottom of the cavity; mounting anelectronic device sensitive to light or other radiation within thecavity; covering the cavity with a transparent cover supported by theledge; and injecting a sealant material into the at least one channel tosimultaneously adhesively bond the transparent cover to the housingstructure and cover at least a portion of the bottom surface of thecavity.
 17. The method of claim 16, further comprising forming thehousing structure from a mold compound.
 18. The method of claim 16,wherein injecting a sealant material into the at least one channelcomprises injecting the sealant material into a sealant well comprisinga notch adjacent to a junction of the ledge and the at least onechannel.
 19. The method of claim 16, further comprising applying avacuum to the cavity.